In a paper about Plato's Timaeus I came across a cryptic note saying: "Academic research usually avoids noting that Plato's assertion about water consisting of two parts air and one part fire is strikingly similar to the modern chemical formula (H2O)." Most obviously this refers to the text found at the end of 56d:
water.. is capable of becoming a compound of one corpuscle of fire with two of air
The Timaeus famously linked the the four elements with regular solids, water being the icosahedron (20 faces), air - the octahedron (8), fire - the tetrahedron (4), so the count is good: $20= 2\times8 +4$. The modern formula for water H2O has been established early in the 19th century. Who was the first to note this coincidence and what later comments are there?